The arrival of affordable, high-performance client SSDs gave us two (closely related) things: 1) a high-speed primary storage option that could work in both a notebook or a desktop, and 2) independence from traditional hard drive form factors.

Unlike traditional hard drives, solid state storage didn't have the same correlation between performance and physical size. The 2.5" form factor was chosen initially because of the rising popularity of notebooks and the fact that desktops could use a 2.5" drive with the aid of a cheap adapter. Since then, many desktop cases now ship with 2.5" drive bays.

It turns out that even the 2.5 wide, 9.5mm tall form factor was a bit overkill for many SSDs. We saw the first examples of this with the arrival of drives from Corsair and Kingston, where the majority of the 2.5" enclosure went unused. Intel and others also launched 1.8" versions of their SSDs with performance levels comparable to their 2.5" counterparts.

Moore's Law ensures that large SSDs can be delivered in small packages. Take the original Intel X25-M for example. The first 80GB and 160GB drives used a 50nm 4GB MLC NAND die (1 or 2 die per package), across twenty packages. Intel's SSD 320, on the other hand, uses 25nm NAND to deliver 300GB or 600GB of storage in the same package configuration. As with all things Moore's Law enables, you can scale in both directions - either increase capacity in a 2.5" form factor, or enable smaller form factors with the same capacity.

The Ultrabook movement has encouraged development of the latter. While Apple and ASUS (among others) have picked custom form factors for their smallest form factor SSDs, there's always a need for standardization. One option is the mSATA form factor: